The template codes are from ISO 639-1 (two letter codes) and ISO 639-3 (3 letter codes). Where a language has both, the use of the two-letter code is preferred. There are also some codes used within the WMF projects for languages that have not yet been coded by ISO, for example {{fiu-vro}}. ISO 639-2 also defines some three letter codes; it defines "T" (terminology) codes which are all included in 639-3; and it defines twenty-two "B" (bibliographic) codes, not included in 639-3. The "B" codes are not used in the wiktionary.